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Names | |||
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Preferred IUPAC name
Trimethylborane
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Other names
Trimethylborine
Trimethylboron | |||
Identifiers | |||
3D model (
JSmol)
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ChemSpider | |||
ECHA InfoCard | 100.008.926 | ||
EC Number |
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PubChem
CID
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CompTox Dashboard (
EPA)
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Properties | |||
C3H9B | |||
Molar mass | 55.92 g/mol | ||
Appearance | Colorless gas or liquid | ||
Density | 0.625 g/cm3 at −100 °C [3] | ||
Melting point | −161.5 °C (−258.7 °F; 111.6 K) | ||
Boiling point | −20.2 °C (−4.4 °F; 253.0 K) | ||
Slight, highly reactive | |||
Structure | |||
Δ | |||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards
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Spontaneously flammable in air; causes burns | ||
GHS labelling: | |||
Danger | |||
H220, H250, H280, H314 | |||
P210, P222, P260, P264, P280, P301+P330+P331, P302+P334, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P370+P378, P377, P381, P403, P405, P410+P403, P422, P501 | |||
Flash point | Not applicable, pyrophoric gas | ||
−40 °C (−40 °F; 233 K) [4] | |||
Safety data sheet (SDS) | MSDS from Voltaix | ||
Related compounds | |||
Related compounds
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Except where otherwise noted, data are given for materials in their
standard state (at 25 °C [77 °F], 100 kPa).
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Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representing methyl).
As a liquid it is colourless. The strongest line in the infrared spectrum is at 1330 cm−1 followed by lines at 3010 cm−1 and 1185 cm−1.
Its melting point is −161.5 °C, and its boiling point is −20.2 °C.
Vapour pressure is given by log P = 6.1385 + 1.75 log T − 1393.3/T − 0.007735 T, where T is temperature in kelvins. [5] Molecular weight is 55.914. The heat of vapourisation is 25.6 kJ/mol. [4]
Trimethylborane was first described in 1862 by Edward Frankland, [6] who also mentioned its adduct with ammonia. [7] Due to its dangerous nature the compound was no longer studied until 1921, when Alfred Stock and Friedrich Zeidler took advantage of the reaction between boron trichloride gas and dimethylzinc. [8] Although the substance can be prepared using Grignard reagents the output is contaminated by unwanted products from the solvent. Trimethylborane can be made on a small scale with a 98% yield by reacting trimethylaluminium in hexane with boron tribromide in dibutyl ether as a solvent. [5] Yet other methods are reacting tributyl borate with trimethylaluminium chloride, or potassium tetrafluoroborate with trimethylaluminium, [9] or adding boron trifluoride in ether to methyl magnesium iodide. [10]
Trimethylborane spontaneously ignites in air if the concentration is high enough. It burns with a green flame producing soot. [11] Slower oxidation with oxygen in a solvent or in the gas phase can produce dimethyltrioxadiboralane, which contains a ring of two boron and three oxygen atoms. However the major product is dimethylborylmethylperoxide, which rapidly decomposes to dimethoxymethylborane. [12]
Trimethylborane is a strong Lewis acid. B(CH3)3 can form an adduct with ammonia: (NH3):B(CH3)3. [13] as well as other Lewis bases. The Lewis acid properties of B(CH3)3 have been analyzed by the ECW model yielding EA= 2.90 and CA= 3.60. When trimethylborane forms an adduct with trimethylamine, steric repulsion between the methyl groups on the B and N results. The ECW model can provide a measure of this steric effect.
Trimethylborane reacts with water and chlorine at room temperature. It also reacts with grease but not with teflon or glass. [5]
Trimethylborane reacts with diborane to disproportionate to form methyldiborane and dimethyldiborane: (CH3)BH2.BH3 and (CH3)2BH.BH3.
It reacts as a gas with trimethylphosphine to form a solid Lewis salt with a heat of formation of −41 kcal per mol. This adduct has a heat of sublimation of −24.6 kcal/mol. No reaction occurs with trimethylarsine or trimethylstibine. [10]
Methyl lithium reacting with the Trimethylborane produces a tetramethylborate salt: LiB(CH3)4. [14] The tetramethylborate ion has a negative charge and is isoelectronic with neopentane, tetramethylsilane, and the tetramethylammonium cation.
Trimethylborane has been used as a neutron counter. [15] For this use it has to be very pure. [13] It is also used in chemical vapour deposition where boron and carbon need to be deposited together.